Surface grinder



1956 LA ROY E. ROBINSON ETAL 3,281,994

SURFACE GRINDER Filed May 22, 1964 6 Sheets-Sheet l Nov- 1, 1966 LA ROY E. ROBINSON ETAL 3,281,994

SURFACE GRINDER 6 Sheets-Sheet 2 Filed May 22, 1964 FHT Hll film/ail". [Mind Nov, 1, 1966 LA ROY E. ROBINSON ETAL 3,281,994

SURFACE GRINDER 6 Sheets-Sheet 5 Filed May 22, 1964 3/ MIN\MUM STROKE J MAXI MUM STROKE .5 [771 .0 ylfiabzzzim Nov. 1, 1966 LA ROY E. ROBINSON ETAL 3,281,994

SURFACE GRINDER Filed May 22, 1964 6 Sheets-Sheet 4 (J /9 RESERVOIR WORK TABLE 'SMMW .23 2221 0 2 1.72 272222252222 Nov. 1, 1966 LA ROY E. ROBINSON ETAL 3,281,994

sunmcz: GRINDER Filed May 22, 1964 6 Sheets-Sheet 5 WORK TABLE 21 I0 Nov. 1, 1966 Filed May 22, 1964 LA ROY E. ROBINSON ETAL SURFACE GRINDER 6 Sheets-Sheet 6 WORK TABLE WORK WORK TABLE @MMM liflayl". 2222222225022 [222 2 1253 512 22-2220 United States Patent 3,281,994 SURFACE GRINDER La Roy E. Robinson, Hopkins, and Charles E. Cleland, Minneapolis, Minn, assignors to (Iontinental Machines, line, Savage, Minn, a corporation of Minnesota Filed May 22, 1964, Ser. No. 369,546 8 Claims. (Cl. l92) This invention relates to surface grinders, and especially to such grinders wherein the work to be ground is mounted on a reciprocatory carriage or table to be carried back and forth beneath a power-driven grinding wheel which is superimposed above the carriage or table and revolves about a horizontal axis.

During the past several years, the design and construction of grinders of this type has been steadily improved to the point where they can now be truly classed as highly precision machine tools. Using standard grinding wheels, these grinders can produce a surface finish better than ten microinches R.M.S., as determined on a type Q Profilometer.

It has been found, however, that the surface produced by these precision surface grinders has a visually discernible regular pattern, and although the presence of the pattern does not mean that the ground surface is in anywise lacking in smoothness or flatness, it has been so taken. Many people, and-most significantly-many executives charged with the responsibility of deciding which of the available machine tools, including grinders, will be purchased, regard the presence of such visually discernable regular patterns in the ground surface as proof positive that the grinder which produced that surface lacks the desired precision. The psychological impact which this condition had upon the sale of these machines was very real and constituted a serious handicap.

With a view toward overcoming this psychological disadvantage, it is the purpose and object of this invention to provide a precision surface grinder with means which will avoid the formation of a visually discernable regular pattern in the surface ground thereon.

It is also an object of this invention to provide means for avoiding the formation of a regular pattern in the ground surface, which in nowise complicates the grinder, and which can be incorporated in the machine without in anywise affecting its precision and accuracy and at very little, if any, additional cost.

As a preface to the description of the invention which follows, it may be helpful to point out that the discovery of what caused the objectionable regular pattern in the ground surface was more elusive than finding a way to cure the defect, once the cause was known. Even after years of experience in the design and manufacture of surface grinders, neither the inventors nor their associates at the plant of their assignee knew why the pattern Was being formed. Finally, after many failures in their attempts to find a solution to the problem, it was deduced that the regular pattern in the ground surface resulted from the fact that each time contact between the grinding wheel and the work was remade-as the direction of traverse was reversedthe contact occurred at the same spot on the wheel-or, if there was a change in this respectthe change followed a regular pattern. Once this discovery was made, it appeared reasonably certain that the objectionable condition would be overcome if unpredictability were substituted for regularity in the engagement of the grinding wheel surface with the work at each reversal in the direction of traverse. Experience has demonstrated that this assumption was correct.

It has been found also, that such unpredictability can be achieved in any one of several different ways. It can be done by:

(l) unpredictably varying the length of the stroke of the work table or carriage;

(2) unpredictably varying the rate of travel of the work table or carriage; or I (3) unpredictably varying the speed of the grinding wheel;

and each of these functions can be accomplished with specifically different structures, several of which are illustrated in the accompanying drawings, in which:

FIGURE 1 is a perspective view of a surface grinder representative of the type with which this invention is concerned, and equipped with means to unpredictably vary the stroke of the work table or carriage;

FIGURE 2 is a fragmentary detail perspective view of a portion of the grinder shown in FIGURE 1, illustrating particularly the manner in which traverse of the workcarrying carriage or table is reversed at unpredictably different points in its traverse so that the length of each traverse is slightly and unpredictably different from the next;

FIGURE 3 is a cross sectional view through FIGURE 5 on the plane of the line 33;

FIGURES 4, 5 and 6 are plan views of the shiftable control member which forms part of the traverse reversing mechanism, and one of the dogs which cooperates therewith, showing the same in three successive positions and illustrating how the effective location of the dog changes during its encounter with the control member;

FIGURE 7 is a diagrammatic view illustrating the manner in which shifting of the effective locations of the two dogs can vary the stroke of the Work table or carriage between minimum and maxi-mum distances;

FIGURE 8 is a diagrammatic view illustrating the embodiment of the invention employed in the grinder shown in FIGURE 1, wherein the shifting of the effective locations of the dogs of the carriage reversing means unpredictably varies the length of the stroke of the work carrying carriage or table;

FIGURE 9 is a diagrammatic view illustrating one way in which the speed of the grinding wheel can be unpredictably varied to prevent the formation of a visually discernable or recognizable pattern in the ground surface;

FIGURE 10 is a diagrammatic view illustrating another embodiment of this invention wherein the rate of travel of the work-carrying carriage is unpredictably varied to achieve the desired result;

FiGURE ll is a diagrammatic view illustrating part of that embodiment of the invention shown in FIGURE 13, but showing another way in which the rate of travel of the work-carrying carriage may be unpredictably varied;

FIGURE 12 is a diagrammatic view illustrating another embodiment of this invention, which is characterized by applying a braking action to the Work-carrying carriage at unpredictable intervals to unpredictably vary its rate of travel; and

FEGURE 13 is a diagrammatic view illustrating another way in which the speed of the grinding wheel may be varied.

Referring now particularly to the accompanying drawings, and directing attention to FIGURE 1, the numeral 5 designates the base of a precision surface grinder of the type with which this invention is concerned. Mounted at the back of the base is a vertically adjustable column, indicated generally by the numeral 6. The grinding Wheel 7 and its drive motor 8 are mounted on this column so that, by lowering or raising the column, the wheel may be fed toward or from the surface of the work to be ground, it being understood that the wheel turns about a horizontal axis and that the workpiece W is positioned beneath the wheel and traversed back and forth transversely of the wheel axis.

To support the workpiece in a manner enabling all portions of its upper face to be brought into work-performing engagement with the grinding wheel, the base has a saddle 11 mounted thereon for translatory horizontal in and out motion, and a work table or carriage 12 is mounted on the saddle for back and forth traverse transversely of the grinding wheel axis.

The saddle 11 is moved in and/or out by conventional cross feed mechanism, and the work table or carriage 12 is reciprocated by a fluid pressure motor 13, not illustrated in FIGURE 1 but shown in the diagrammatic views, FIGURES 8, 10, and 12.

The work is held in position on the table or carriage 12 by means of a conventional magnetic chuck (not shown) and the vertical position of the grinding wheel with respect to the work is controlled by conventional downfeed mechanism which need not be described, but which adjusts the column 6 up or down as required.

The direction of work table or carriage traverse, and also the limits of its traverse, are controlled by a reversing mechanism which includes a pair of left and righthand dogs 14 and 15 mounted on the work table or carriage and a reversing lever 16 mounted on the saddle 11 to rotate about a vertical axis with a portion thereof projecting into the paths of the dogs 14 and 15, which thus collide with the lever and rotate the same one way or the other depending upon which of the dogs engages it.

The rocking of the lever 16 about its axis actuates a control valve 17 which, as shown in FIGURES 8, 10 and 12, acts to reverse the hydraulic connections between a pilot valve 18 and a pressure source 19. The pilot valve 18, in turn, controls the flow of pressure fluid to the hydraulic cylinder 13.

Inasmuch as this hydraulic system which powers the work table or carriage and effects its traverse, is conventional, further description thereof is not necessary to an understanding of this invention, it being sufficient to point out that the piston 20 in the hydraulic cylinder is suitably connected with the work table or carriage, as indicated at 21 in the diagrammatic views, FIGURES 8, 10 and 12.

Obviously, the location of the dogs 14 and 15 on the work table or carriage governs the length of its stroke, and to enable complete traverse of the work surface past the grinding wheel as the table or carriage carries the work back and forth, the dog 14 should be located to the left of the adjacent edge of the work surface, and the dog 15 to the right of its respective edge of the work surface. At this point it would be well to note that with each reversal in the direction of work traverse, contact between the work and the grinding wheel is broken and re-made.

To enable the dogs 14 and 15 to be properly positioned with respect to the workpiece, a T-slot 23 is formed in the front face 24 of the table or carriage and the dogs have guide lugs slidably received in this slot. Hence the dogs may be slid along the length of the slot and secured in any selected position by tightening clamping screws 25.

In a conventional surface grinder, the dogs 14 and 15 have fixed abutments located at different elevations to engage one or the other of two ears 26 or 27, which project divergently from the hub of the reversing lever 16 and likewise are at different levels so that the dog which engages one of them will not engage the other, and vice versa.

In that embodiment of the invention illustrated in FIG- URES 1, and 2-8, inclusive, the effect of the carriage or work table reversing means is unpredictably modified to unpredictably vary the stroke of the carriage or work table. This is accomplished by substituting freely rotatable eccentrically mounted rollers 30 and 31 for the conventional fixed abutments on the dogs. Because of their eccentric mounting, each encounter of these rollers with their respective ears 26 and 27 on the reversing lever, brings about an unpredictable degree of rotation of the rollers. This rotation of the rollers is shown in FIGURES 4, 5 and 6, by the changed location of a dot 32 placed upon the roller for illustrative purposes.

Because of the rotation of the rollers 30-31 as they collide with their respective ears 26-27 and rock the control member, the effective location of the dogs and hence the point in the traverse of the work at which the dogs act to reverse the direction of traverse, varies unpredictably. This means that the stroke of the work table or carriage will vary unpredictably between minimum and maximum distances, as exaggeratedly illustrated in FIG- URE 7.

The described unpredictable variation in length of stroke which results from modifying the effect of the carriage reversing means, as described, avoids the formation of a visually discernable pattern in the surface being ground, since it results in the initial contact between the work and the wheel being remade at a different spot on the periphery of the grinding wheel with each reversal in direction of traverse. Another way of continually and unpredictably changmg the spot on the surface of the wheel which first comes into contact with the work every time contact is remade is by unpredictably varying the speed of rotation of the wheeland one way of doing this is illustrated in FIG- URE 9. As here shown, the motor 8 which drives the wheel is connected to its power source through a solenoid actuated switch 35, which may be normally closed-as shown in FIGURE 9-and opened whenever its solenoid 36 is energized. Energization of the solenoid is controlled by an irregularly shaped cam 37 which is driven by a motor 38 and actuates a switch 39 in the circuit for the solenoid 36. As the cam rotates, the switch is momentarily opened at irregularly spaced intervals.

Unpredictably varying the rate of traverse of the work table or carriage is another way in which the formation of a visually discernable regular pattern in the surface being ground can be avoided, and in FIG. 10 one way of varying the rate of table motion is illustrated. As here shown, a solenoid valve 40 is connected in the hydraulic circuit of the fluid pressure motor 13. This valve is opened and closed by means of a solenoid 41 which, in turn, is energized at intervals at the dictation of an irregularly shaped motor driven cam 42.

FIGURE 11 illustrates what might be considered a modification of the structure shown in FIGURE 10. Here the solenoid valve 40 is connected in the line which supplies the pilot valve 18, to speed up or slow down the response of the pilot valve. Obviously, the slower the pilot valve acts, the longer the over travel of the workcarrying table would be. Hence this system provides a random stroke length.

Random table speed or rate of traverse is another way in which the desired results may be accomplished and, in FIGURE 12, one way of unpredictably varying the rate of traverse is illustrated. As here shown, a brake 45 under the control of a solenoid 46 acts directly upon the work table or carriage to vary its rate of travel. Energization of the solenoid 46, as in the previous embodiments of the invention, is governed by an irregularly shaped motordriven rotating cam 47.

FIGURE 13 illustrates how a directly applied braking action may be employed to unpredictably vary the speed of the grinding wheel. In this case a brake band 50 wrapped around a brake drum 51 which is fixed to the shaft of the grinding wheel, is tightened whenever a solenoid 52 in energized, and the energization of this solenoid, as before, can be under the control of an irregularly shaped rotating cam.

From the foregoing description, taken in connection with the accompanying drawings, it will be apparent to those skilled in this art that this invention eliminates or avoids the formation of a visually discernable or recognizable regular pattern in the surface of work ground on a truly precision surface grinder, and-in doing so-overcomes the very serious phychological disadvantage which heretofore confronted makers of such precision machines. It will also be apparent that, while several specific embodiments of the invention have been illustrated and described, the invention is not limited thereto, but instead encompases all structures and ways of achieving the desired results as come Within the scope of the claims.

What is claimed as our invention is:

1. In a surface grinder wherein a rotary power driven grinding tool member and a work-carrying member are mounted and arranged to have relative reciprocatory work-performing traverse and the length of said traverse is greater than the length of the work surface along the line of traverse, so that contact between the grinding tool and the work is repeatedly broken and remade as the direction of relative traverse changes, the combination of:

(A) power means to drive the rotary grinding tool member;

(B) power means to reciprocate one of said members with respect to the other;

(C) reversing means operatively connected with the power means which effects the reciprocation, and arranged to be acted upon by the reciprocated member when work-performing contact between the grinding tool and the work is broken, to reverse the direction said power means moves the reciprocatory member; and

(D) modifying means to unpredictably modify the effect which one of said three means has upon its respective structure, to thereby unpredictably vary the point on the periphery of the rotary grinding tool which first makes contact with the work surface each time contact therebetween is remade, so as to avoid the formation of a visually discernable regular pattern on the ground surface of the work.

2. In a surface grinder, the combination of claim 1, wherein said modifying means haphazardly varies the length of the stroke of the reciprocatory member.

3. In a surface grinder, the combination of claim 2, wherein it is the reversing means upon which the modifying means acts to haphazardly vary the length of the stroke of the reciprocatory member.

4. In a surface grinder, the combination of claim 3, wherein the reversing means comprises:

a shiftable control member; and a pair of dogs mounted on the reciprocatory member to collide with and thereby actuate the shiftable control member, and wherein the portion of said dogs which collides with the shiftable control member is an eccentrically freely rotatably mounted roller so positioned that the periphery thereof collides with the shiftable control member, whereby with each such collision the roller has an unpredictable degree of rotation imparted to it. 5. In a surface grinder, the combination of claim 1; wherein said modifying means comprises:

means operatively associated with the reversing means to unpredictably vary the instant said reversing means effects reversal of the direction of traverse, whereby the length of successive strokes of the reciprooatory member is unpredictably varied. 6. In a surface grinder, the combination of claim 1, wherein said modifying means comprises:

means operatively associated with one of said two power means to unpredictably vary the rate at which it drives its respective structure. 7. In a surface grinder, the combination of claim 1, wherein said modifying means includes means to unpredictably modify the effect which the power means for the rotary grinding tool has upon it, so that the speed at which the tool rotates is unpredictably varied. 8. In a surface grinder, the combination of claim 1, wherein said modifying means includes means to unpredictably modify the effect which the power means that drives the reciprocatory member has upon it, so that the rate at which said member moves is unpredictably varied.

No references cited.

ROBERT C. RIORDON, Primary Examiner.

L. S. SELMAN, Assistant Examiner. 

1. IN A SURFACE GRINDER WHEREIN A ROTARY POWER DRIVEN GRINDING TOOL MEMBER AND A WORK-CARRYING MEMBER ARE MOUNTED AND ARRANGED TO HAVE RELATIVE RECIPROCATORY WORK-PERFORMING TRANSVERSE AND THE LENGTH OF SAID TRANSVERSE IS GREATER THAN THE LENGTH OF THE WORK SURFACE ALONG THE LINE OF TRANSVERSE, SO THAT CONTACT BETWEEN THE GRINDING TOOL AND THE WORK IS REPEATEDLY BROKEN AND REMADE AS THE DIRECTION OF RELATIVE TRAVERSE CHANGES, THE COMBINATION OF: (A) A POWER MEANS TO DRIVE THE ROTARY GRINDING TOOL MEMBER; (B) POWER MEANS TO RECIPROCATE ONE OF SAID MEMBERS WITH RESPECT TO THE OTHER; (C) REVERSING MEANS OPERATIVELY CONNECTED WITH THE POWER MEANS WHICH EFFECTS THE RECIPROCATION, AND ARRANGED TO BE ACTED UPON BY THE RECIPROCATED MEMBER WHEN WORK-PERFORMING CONTACT BETWEEN THE GRINDING TOOL AND THE WORK IS BROKEN, TO REVERSE THE DIRECTION SAID POWER MEANS MOVES THE RECIPROCATORY MEMBER; AND 